15. E M B R Y O G E N E S I S in vitro
539
Potenz"), and the area of the primary inducer. It may be noted, that
the marginal zone alone, corresponding to the chordo-mesodermal
area, has multiple possibilities of self-differentiation (Fig. 5b). But the
whole ectodermal anlage is endowed with the same properties of
differentiation, when it is subjected to the appropriate inducing factors.
That is what Fig. 5c shows—there one sees that the endodermal
FIG. 5. Comparison of the developing parts of the young gastrula with regard to: (a) their
prospective fate; (b) their powers of self-differentiation; (c) their prospective potentialities;
(d) the primary induction field. ® Epidermis; ® medullary plate; © notochord; + somitic and
lateral mesoderm; lilll intestine and derivatives. (After Holtfreter, 1936.)
anlage alone is strictly determined. Moreover, this area is not alone in
being able to differentiate the tissues of the intestine and of its derivatives, because the ectoderm itself can give rise to endodermal derivatives when it is cultured in the presence of the appropriate mesodermal
inducer (Takata and Yamada, 1960).
C. T E S T I N G T H E I N D U C I N G P O W E R OF TISSUES A N D OF
E X T R A C T S IN IN VITRO
C U L T U R E
Coincident with research on the whole embryo, many experiments
have been done on cultures in vitro, in Holtfreter's solution, by the
a
b
c
d